[c-nsp] quick spanning tree question

Yuri Bank yuribank at gmail.com
Tue Mar 30 02:06:30 EDT 2010


What about your other TOR switch? If it has elected Switch 3 as its root,
that would explain why traffic is being forwarded over that link.


Can we see output from your other switches?


-Yuri

On Mon, Mar 29, 2010 at 9:58 PM, Cord MacLeod <cordmacleod at gmail.com> wrote:

>
> On Mar 29, 2010, at 9:06 PM, Octavio Alvarez wrote:
>
> > On Fri, 26 Mar 2010 23:47:47 -0700, Cord MacLeod <cordmacleod at gmail.com>
> wrote:
> >
> >> 3 days ago traffic started showing up on the trunk port connecting my
> top of rack switches.  Each of these switches has it's own better trunk path
> to the root bridge.  I can't see why any traffic at all would traverse these
> links unless the other trunk on g0/45 was down, which it isn't.  Also,
> spanning tree doesn't claim any topology changes.
> >
> > There's very little information. I could even think your traffic is
> > real and STP doesn't have anything to do with it.
>
> Sorry for the late reply.  Here is some more information.  First, the
> traffic is over 50mbit, I don't think it's STP.  Second:
>
> switch3#show spanning-tree interface g0/46
>
> Vlan             Role Sts Cost      Prio.Nbr Type
> ---------------- ---- --- --------- --------
> --------------------------------
> VLAN0001         Desg FWD 4         128.46   P2p
> VLAN0100         Desg FWD 4         128.46   P2p
> VLAN0101         Desg FWD 4         128.46   P2p
> VLAN0102         Altn BLK 4         128.46   P2p
> VLAN0120         Desg FWD 4         128.46   P2p
> VLAN0200         Desg FWD 4         128.46   P2p
> VLAN0231         Desg FWD 4         128.46   P2p
> VLAN0250         Desg FWD 4         128.46   P2p
> VLAN0321         Desg FWD 4         128.46   P2p
> VLAN0450         Desg FWD 4         128.46   P2p
> VLAN0777         Desg FWD 4         128.46   P2p
> VLAN0888         Desg FWD 4         128.46   P2p
>
> switch3#sh spanning-tree root
>
>                                         Root    Hello Max Fwd
> Vlan                   Root ID          Cost    Time  Age Dly  Root Port
> ---------------- -------------------- --------- ----- --- ---  ------------
> VLAN0001         24577 0017.e0d7.e180         4    2   20  15  Gi0/45
> VLAN0100         24676 0017.e0d7.e180         4    2   20  15  Gi0/45
> VLAN0101         24677 0017.e0d7.e180         4    2   20  15  Gi0/45
> VLAN0102         20582 0018.181b.d700         7    2   20  15  Gi0/45
> VLAN0120         24696 0017.e0d7.e180         4    2   20  15  Gi0/45
> VLAN0200         24776 0017.e0d7.e180         4    2   20  15  Gi0/45
> VLAN0231         24807 0017.e0d7.e180         4    2   20  15  Gi0/45
> VLAN0250         24826 0017.e0d7.e180         4    2   20  15  Gi0/45
> VLAN0321         24897 0017.e0d7.e180         4    2   20  15  Gi0/45
> VLAN0450         25026 0017.e0d7.e180         4    2   20  15  Gi0/45
> VLAN0777         25353 0017.e0d7.e180         4    2   20  15  Gi0/45
> VLAN0888         25464 0017.e0d7.e180         4    2   20  15  Gi0/45
>
> switch3#show spanning-tree summary
> Switch is in pvst mode
> Root bridge for: none
> Extended system ID           is enabled
> Portfast Default             is disabled
> PortFast BPDU Guard Default  is disabled
> Portfast BPDU Filter Default is disabled
> Loopguard Default            is disabled
> EtherChannel misconfig guard is enabled
> UplinkFast                   is disabled
> BackboneFast                 is disabled
> Configured Pathcost method used is short
>
> Name                   Blocking Listening Learning Forwarding STP Active
> ---------------------- -------- --------- -------- ---------- ----------
> VLAN0001                     0         0        0          2          2
> VLAN0100                     0         0        0          9          9
> VLAN0101                     0         0        0          2          2
> VLAN0102                     1         0        0          1          2
> VLAN0120                     0         0        0         19         19
> VLAN0200                     0         0        0         16         16
> VLAN0231                     0         0        0          2          2
> VLAN0250                     0         0        0          2          2
> VLAN0321                     0         0        0          5          5
> VLAN0450                     0         0        0          2          2
> VLAN0777                     0         0        0          2          2
> VLAN0888                     0         0        0          2          2
> ---------------------- -------- --------- -------- ---------- ----------
> 12 vlans                     1         0        0         64         65
>
> switch3#show int g0/46
> GigabitEthernet0/46 is up, line protocol is up (connected)
> ...
>  MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec,
>     reliability 255/255, txload 5/255, rxload 1/255
>  Encapsulation ARPA, loopback not set
>  Keepalive not set
>  Full-duplex, 1000Mb/s, link type is auto, media type is 10/100/1000BaseTX
>  input flow-control is off, output flow-control is unsupported
>  ARP type: ARPA, ARP Timeout 04:00:00
>  Last input 00:00:00, output 00:00:00, output hang never
>  Last clearing of "show interface" counters never
>  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
>  Queueing strategy: fifo
>  Output queue: 0/40 (size/max)
>  5 minute input rate 0 bits/sec, 0 packets/sec
>  5 minute output rate 59995000 bits/sec, 3555 packets/sec
>     1446844033 packets input, 479111376008 bytes, 0 no buffer
>     Received 35695615 broadcasts (0 multicasts)
>     0 runts, 0 giants, 0 throttles
>     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
>     0 watchdog, 35604297 multicast, 0 pause input
>     0 input packets with dribble condition detected
>     10988444843 packets output, 4655746445035 bytes, 0 underruns
>     0 output errors, 0 collisions, 1 interface resets
>     0 babbles, 0 late collision, 0 deferred
>     0 lost carrier, 0 no carrier, 0 PAUSE output
>     0 output buffer failures, 0 output buffers swapped out
>
>
> Does this give enough information?  From my understanding of spanning tree,
> g0/46 should not be used for any traffic.  g0/45 is the root port for all
> vlans.
>
>
>
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